Patch "x86/pkeys/selftests: Avoid printf-in-signal deadlocks" has been added to the 4.16-stable tree

This is a note to let you know that I've just added the patch titled

x86/pkeys/selftests: Avoid printf-in-signal deadlocks

to the 4.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-pkeys-selftests-avoid-printf-in-signal-deadlocks.patch
and it can be found in the queue-4.16 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Dave Hansen <[email protected]>
Date: Wed, 9 May 2018 10:13:44 -0700
Subject: x86/pkeys/selftests: Avoid printf-in-signal deadlocks

From: Dave Hansen <[email protected]>

[ Upstream commit caf9eb6b4c82fc6cbd03697052ff22d97b0c377b ]

printf() and friends are unusable in signal handlers. They deadlock. The pkey selftest does not do any normal printing in signal handlers, only extra debugging. So, just print the format string so we get *some* output when debugging.

---
 tools/testing/selftests/x86/pkey-helpers.h |   20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

@@ -26,30 +26,26 @@ static inline void sigsafe_printf(const
 {
 	va_list ap;
 
-	va_start(ap, format);
 	if (!dprint_in_signal) {
+		va_start(ap, format);
 		vprintf(format, ap);
+		va_end(ap);
 	} else {
 		int ret;
-		int len = vsnprintf(dprint_in_signal_buffer,
-				    DPRINT_IN_SIGNAL_BUF_SIZE,
-				    format, ap);
 		/*
-		 * len is amount that would have been printed,
-		 * but actual write is truncated at BUF_SIZE.
+		 * No printf() functions are signal-safe.
+		 * They deadlock easily. Write the format
+		 * string to get some output, even if
+		 * incomplete.
 		 */
-		if (len > DPRINT_IN_SIGNAL_BUF_SIZE)
-			len = DPRINT_IN_SIGNAL_BUF_SIZE;
-		ret = write(1, dprint_in_signal_buffer, len);
+		ret = write(1, format, strlen(format));
 		if (ret < 0)
-			abort();
+			exit(1);
 	}
-	va_end(ap);
 }
 #define dprintf_level(level, args...) do {	\
 	if (level <= DEBUG_LEVEL)		\
 		sigsafe_printf(args);		\
-	fflush(NULL);				\
 } while (0)
 #define dprintf0(args...) dprintf_level(0, args)
 #define dprintf1(args...) dprintf_level(1, args)

Patches currently in stable-queue which might be from [email protected] are

queue-4.16/x86-pkeys-selftests-factor-out-instruction-page.patch queue-4.16/x86-pkeys-selftests-fix-pointer-math.patch queue-4.16/x86-pkeys-selftests-adjust-the-self-test-to-fresh-distros-that-export-the-pkeys-abi.patch queue-4.16/x86-pkeys-selftests-add-a-test-for-pkey-0.patch queue-4.16/x86-pkeys-selftests-stop-using-assert.patch queue-4.16/x86-pkeys-selftests-save-off-prot-for-allocations.patch queue-4.16/x86-pkeys-selftests-remove-dead-debugging-code-fix-dprint_in_signal.patch queue-4.16/x86-mpx-selftests-adjust-the-self-test-to-fresh-distros-that-export-the-mpx-abi.patch queue-4.16/x86-pkeys-selftests-add-prot_exec-test.patch queue-4.16/x86-pkeys-selftests-allow-faults-on-unknown-keys.patch queue-4.16/x86-pkeys-selftests-give-better-unexpected-fault-error-messages.patch queue-4.16/x86-pkeys-selftests-avoid-printf-in-signal-deadlocks.patch queue-4.16/x86-pkeys-selftests-fix-pkey-exhaustion-test-off-by-one.patch